Plutonium

For some reason when i jump and hold down the spacebar, i float. and also take almost no fall damage, this is a pain and i don't want this. and i can't even use the paralyzer, i've been playing for 10 years, i know i'm doing it right but it won't go any higher than i show here https://youtu.be/szwIHbH2a_E. gravity settings are all at default i checked myself, and this only happens on custom games